Photoresist stripping solution and a method of stripping photoresists using the same

ABSTRACT

A photoresist stripping solution comprising (a) a specified quaternary ammonium hydroxide, such as tetrabutylammonium hydroxide, tetrapropylammonium hydroxide, methyltributylammonium hydroxide or methyltripropylammonium hydroxide, (b) a water-soluble amine, (c) water, (d) a corrosion inhibitor and (e) a water-soluble organic solvent, the compounding ratio of component (a) to component (b) being in the range of from 1:3 to 1:10 by mass, as well as a method of stripping photoresists using the solution. The stripping solution of the invention assures effective protection of Al, Cu and other wiring metal conductors against corroding as well as efficient stripping of the photoresist film, post-ashing residues such as modified photoresist film and metal depositions. It also assures efficient stripping of Si-based residues and effective protection of the substrate (particularly the reverse side of a Si substrate) from corroding.

This is a continuation of U.S. patent application Ser. No. 11/232,986,filed Sep. 23, 2005, which is a continuation of U.S. patent applicationSer. No. 10/925,978, filed Aug. 26, 2004, now abandoned, which is acontinuation of Ser. No. 10/208,054, filed Jul. 31, 2002, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photoresist stripping solution and a methodof stripping photoresists using the same. The invention is suitable foruse in the fabrication of semiconductor devices such as ICs and LSIs, aswell as liquid-crystal panel apparatus.

2. Description of Relevant Art

The fabrication of semiconductor devices such as ICs and LSIs, as wellas liquid-crystal panel apparatus, comprises forming a uniformphotoresist coating over conductive metallic layers, insulation layerssuch as an SiO₂ film formed on a substrate (silicon wafer) by CVD;performing selective exposure and development to form a photoresistpattern; selectively etching the substrate having the conductivemetallic layers, the insulation layers formed thereon by CVD, using thephotoresist pattern as a mask to thereby form a microcircuit; and thenremoving the unwanted photoresist layer with a stripping solution.

With the recent tendency toward highly integrated, high-densitycircuits, dry etching enabling fine etching with a higher density hasbecome the major means. Also, it has been a practice to employ plasmaashing to remove the unnecessary photoresist layers remaining afteretching. After these etching and ashing treatments, residues comprisingmodified photoresist films and other components, referred to horn-likeshaped “veil”, “fences” or “side-walls”, remain on the bottom or sidewall of patterned grooves. In addition, etching of metallic layers andashing treatment builds up metal depositions. Such post-ashing residuesor depositions should be completely stripped away so as to keep goodyields in the production of semiconductors.

In particular, as the degree of integration of semiconductor devicesincreases and the chip size decreases, efforts are recently being madeto reduce the feature size of wiring circuits while fabricating them inan increasing number of superposed layers. A problem with this approachis that wiring delay is caused by the resistance of the metal films used(wiring resistance) and wiring capacity. To deal with this problem, ithas been proposed to use metals such as copper (Cu) that have smallerresistance than aluminum (Al) mainly used as a conventional wiringmaterial, and recent models of semiconductor devices can be divided intotwo types, one using Al conductors (Al, Al alloy and other Al-basedmetal wiring) and the other using Cu conductors (Cu-based metal wiring).In addition to the need to prevent devices of these two types fromcorroding, it is also necessary to provide effective protection againstcorrosion of other metals on the devices, and further improvements aredesired to achieve effective stripping away of the photoresist layer andthe post-ashing residues, and to prevent metal conductors fromcorroding.

For critical reasons such as low etching resistance of copper, coppermetal wiring is generally formed by the dual damascene process. Whilevarious methods have been proposed to implement the dual damasceneprocess, one example comprises the following: a Cu layer is formed on asubstrate; a multiple of interlevel films, such as low-dielectric films(e.g. SOG film) and insulation films (e.g. SiN film and SiO₂ film), aresuperposed on the Cu layer; a photoresist layer is provided on thetopmost layer, and selectively exposed and developed to form aphotoresist pattern; with this photoresist pattern used as a mask, thelow-dielectric films, insulation films are etched and subjected toashing treatment to strip away the photoresist pattern while forming viaholes that connect to the Cu layer on the substrate; subsequently,another photoresist layer is formed on the topmost of the remainingsuperposed interlevel films and is selectively exposed and developed toform a new photoresist pattern; with this photoresist pattern used as amask, a specified number of low-dielectric films, insulation films areetched, and subjected to ashing treatment to strip away the photoresistpattern while forming wiring grooves (trenches) that communicate withthe above-described via holes; the via holes and wiring trenches arefilled with Cu by plating or other method, thereby forming multiplelayers of Cu wiring.

In the dual damascene process, Cu-based residues (Cu deposition) areprone to occur as the result of etching and ashing treatments that areeffected to form the via holes; in addition, Si-based residues (Sideposition) originating from the low-dielectric films and insulationfilms are prone to occur as the result of etching and ashing treatmentsthat are effected to form the wiring trenches, and the residues areoccasionally formed as Si deposition around the opening of each trench.Unless the Cu and Si depositions are completely stripped away, problemswill occur such as lower yield of semiconductor fabrication.

Needless to say, the occurrence of Si-based residues (Si deposition)originating from the low-dielectric films and insulation films is notlimited to the case of using the dual damascene process; they can occurin almost all cases of forming metal wiring on the substrate havingSi-based interlevel films thereon.

Thus, in the current photolithographic technology, the photoresiststripping techniques are required to meet increasingly rigorousconditions in order to adjust for the decreasing feature size ofpatterns, the formation of more interlevel layers on the substrate andthe changes in materials formed on the substrate surface. Of course, toensure a good working environment, the photoresist stripping solution tobe used must be not only easy to handle but also less hazardous in suchterms as toxicity and explosiveness.

Under these circumstances, a variety of stripping solutions based onquaternary ammonium hydroxides and water-soluble amines have beenproposed to date as candidates that meet the above-mentioned variousrequirements of stripping photoresists and post-ashing residues (see,for example, JP-A-1-502059, JP-A-6-202345, JP-A-7-28254, JP-A-7-219241,JP-A-8-262746, JP-A-10-289891, JP-A-11-251214, JP-A-2000-164597 andJP-A-2001-22096).

A problem with the stripping solutions proposed in those patents is thatif their ability to strip the photoresist film and post-ashing residues,particularly the ability to strip Si-based residues, is enhanced to anadequate level, they are not capable of providing adequate protectionagainst corrosion of the Si substrate, particularly its reverse side;hence, the ability to strip the Si-based residues must be compromised tosome extent.

However, for successful lithography in today's practice of fabricatingsemiconductor devices with an ever decreasing feature size and anincreasing number of interlevel films superposed on the substrate,stripping of the Si-based residues cannot be compromised and it isdesired to develop a stripping solution that meets both requirements forefficient stripping of Si-based residues and effective protection of theSi substrate from corroding.

A group of stripping solutions that contain hydroxylamines have alsobeen proposed, but the starting materials from which they are made arehighly hazardous (e.g. explosive) and at the stage of purification, theyare not easy to handle since they are toxic or hazardous.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object of providing a photoresist stripping solution thatis suitable for use in the photolithographic technology to form today'ssemiconductor and liquid-crystal display devices having an everdecreasing feature size and an increasing number of interlevel filmssuperposed on the substrate, and that can assure effective protection ofAl, Cu and other wiring metal conductors against corrosion as well asefficient stripping of the photoresist film, post-ashing residues andmetal depositions.

Another object of the invention is to provide a photoresist strippingsolution that is particularly suitable for use in the formation of metalwiring on a substrate overlaid with Si-based interlevel films such asinsulation films (e.g. SiO₂ film) and low-dielectric films (e.g. SOGfilm), and by means of which efficient stripping of Si-based residuesoriginating from these Si-based interlevel films and effectiveprotection of the substrate, particularly the reverse side of an Sisubstrate, from corroding can be accomplished in a balanced way.

The present invention provides a photoresist stripping solutioncomprising (a) a quaternary ammonium hydroxide of the following generalformula (I):

where R₁, R₂, R₃ and R₄ are each independently an alkyl group or ahydroxyalkyl group, provided that at least one of R₁, R₂, R₃ and R₄ isan alkyl or hydroxyalkyl group having at least 3 carbon atoms, (b) awater-soluble amine, (c) water, (d) a corrosion inhibitor and (e) awater-soluble organic solvent, the compounding ratio of component (a) tocomponent (b) being in the range of from 1:3 to 1:10 by mass.

The present invention also provides a method of stripping photoresistswhich comprises forming a photoresist pattern on a substrate, etchingthe substrate using the photoresist as a mask, and thereafter strippingaway the photoresist pattern from the substrate using the photoresiststripping solution as described above.

The present invention furthermore provides a method of strippingphotoresists which comprises forming a photoresist pattern on asubstrate, etching the substrate using the photoresist as a mask, thenplasma ashing the photoresist pattern, and thereafter stripping awaypost-plasma ashing residues from the substrate using the photoresiststripping solution as described above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is described below in detail.

In the invention, component (a) is a quaternary ammonium hydroxide ofthe following general formula (I):

where R₁, R₂, R₃ and R₄ are each independently an alkyl group or ahydroxyalkyl group, provided that at least one of R₁, R₂, R₃ and R₄ isan alkyl or hydroxyalkyl group having at least 3 carbon atoms.

Specifically, the quaternary ammonium hydroxide represented by thegeneral formula (I) is preferably at least one compound selected fromamong tetrabutylammonium hydroxide, tetrapropylammonium hydroxide,methyltributylammonium hydroxide and methyltripropylammonium hydroxide.

In the conventional photoresist stripping solutions, as quaternaryammonium, hydroxidestetramethylammonium hydroxide, tetraethylammoniumhydroxide, methyltriethylammonium hydroxide and dimethyldiethylammoniumhydroxide, etc. have been used. These compounds claim high performancein removing Si-based residues, however, they attack Al, Cu, Si, etc. sostrongly that corrosion, damage and other defects are prone to occur. Incontrast, component (a) in the present invention is not only high in itsability to remove Si-based residues but also mild in its action ofattacking Al, Cu, Si, etc. Therefore, by using component (a), efficientstripping of Si-based residues and effective protection of not only theSi substrate but also wiring metals such as Al and Cu against corrosioncan be achieved in a balanced way, thus providing a more desirablephotoresist stripping solution. Compounds as component (a) can be usedeither singly or in admixture.

The stripping solution of the invention preferably contains component(a) in an amount of 1-20 mass percent, more preferably 2-10 masspercent. If the proportion of component (a) is less than 1 mass percent,the overall stripping ability tends to be insufficient; if theproportion of component (a) is more than 20 mass percent, the substrateis prone to corrode.

Water-soluble amine as component (b) include alkanolamines, such asmonoethanolamine, diethanolamine, triethanolamine,2-(2-aminoethoxy)ethanol, N,N-dimethylethanolamine,N,N-diethylethanolamine, N,N-dibutylethanolamine, N-methylethanolamine,N-ethylethanolamine, N-butylethanolamine, N-methyldiethanolamine,monoisopropanolamine, diisopropanolamine and triisopropanolamine;polyalkylenepolyamines, such as diethylenetriamine,triethylenetetramine, propylenediamine, N,N-diethylethylenediamine,1,4-butanediamine, N-ethyl-ethylenediamine, 1,2-propanediamine,1,3-propanediamine and 1,6-hexanediamine; aliphatic amines, such as2-ethyl-hexylamine, dioctylamine, tributylamine, tripropylamine,triallylamine, heptylamine and cyclohexylamine; aromatic amines, such asbenzylamine and diphenylamine; and cyclic amines, such as piperazine,N-methyl-piperazine, methyl-piperazine and hydroxyethylpiperazine. Amongthese, monoethanolamine, 2-(2-aminoethoxy)ethanol andN-methylethanolamine are preferably used from the viewpoint ofpreventing metal conductors from corrosion. Compounds as component (b)may be used either singly or in admixture.

Component (b) is compounded in a mass 3-10 times, preferably 4-9 times,the mass of component (a). If component (b) is compounded in a mass lessthan 3 times the mass of component (a), the overall stripping ability isinadequate; if component (b) is compounded in a mass more than 10 timesthe mass of component (a), the substrate is not adequately protectedagainst corroding.

Compounds used as component (b) have different strengths of attack onmetals (e.g. Al and Cu) and Si, so it is recommended that they becompounded in a suitably adjusted optimum amount. For instance, ifstrongly corrosive monoethanolamine is used as component (b), it isrecommended to adjust the optimum amount to lie within the range ofabout 3-6 times the mass of component (a); if less corrosive2-(2-aminoethoxy)ethanol is used as component (b), it is preferably usedin an amount about 4-8 times the mass of component (a); if much lesscorrosive N-methylethanolamine is used as component (b), it ispreferably used in an amount about 5-10 times, more preferably about 5-9times, the mass of component (a).

Water as component (c) is incidental to the other components in thestripping solution of the invention but more of it need be added to haveits amount adjusted to meet the purposes of the invention. Component (c)is preferably compounded in an amount of 10-50 mass percent, morepreferably 20-45 mass percent, of the stripping solution of theinvention. If the compounding amount of component (c) is less than 10mass percent, the strippability of residues tends to decrease; if thecompounding amount of component (c) exceeds 50 mass percent, thepossibility for wiring metals such as Al and Cu to corrode is high.

The compounding amount of component (c) is preferably optimizedaccording to the device forming process. Take, for example, thestripping step which is currently performed by any one of dip method,spray method or paddle method. In a process adopting the dip or spraymethod which features a comparatively long time of contact between thephotoresist stripping solution and the substrate, component (c) ispreferably compounded in an amount of about 10-30 mass percent. In aprocess adopting the paddle method which features a comparatively shorttime of contact between the photoresist stripping solution and thesubstrate, component (c) is preferably compounded in an amount of about30-50 mass percent.

The corrosion inhibitor as component (d) is preferably at least onecompound selected from among aromatic hydroxy compounds,benzotriazole-based compounds and mercapto group containing compounds.

The aromatic hydroxyl compounds include phenol, cresol, xylenol,pyrocatechol(=1,2-dihydroxybenzene), tert-butylcatechol, resorcinol,hydroquinone, pyrogallol, 1,2,4-benzenetriol, salicyl alcohol,p-hydroxybenzyl alcohol, o-hydroxybenzyl alcohol, p-hydroxyphenethylalcohol, p-aminophenol, m-aminophenol, diaminophenol, a minoresorcinol,p-hydroxybenzoic acid, o-hydroxybenzoic acid, 2,4-dihydroxybenzoic acid,2,5-dihydroxybenzoic acid, 3,4-dihydroxybenzoic acid,3,5-dihydroxybenzoic acid and gallic acid. Among them, pyrocatechol,pyrogallol and gallic acid, etc. are used with advantage. The aromatichydroxyl compounds may be used either individually or in combination.

The benzotriazole-based compounds include the ones represented by thefollowing general formula (II):

where R₅ and R₆ are each independently a hydrogen atom, a substituted orunsubstituted hydrocarbon group of 1-10 carbon atoms, a carboxyl group,an amino group, a hydroxyl group, a cyano group, a formyl group, asulfonylalkyl group or a sulfo group; Q is a hydrogen atom, a hydroxylgroup or a substituted or unsubstituted hydrocarbon group of 1-10 carbonatoms provided that said hydrocarbon group may have an amide bond orester bond in the structure, an aryl group or the group represented bythe following formula (III):

wherein R₇ represents an alkyl group of 1-6 carbon atoms; and R₈ and R₉are each independently a hydrogen atom, a hydroxyl group or ahydroxyalkyl group or an alkoxyalkyl group of 1-6 carbon atoms.

In the definition of the groups Q, R₅ and R₆ as specified in the presentinvention, each of the hydrocarbon groups may be an aromatic hydrocarbongroup or an aliphatic hydrocarbon group, may be saturated orunsaturated, and may be a linear group or a branched group. Examples ofa substituted hydrocarbon group include hydroxyalkyl groups andalkoxylalkyl groups.

In the case where pure Cu is used as the metal conductor on thesubstrate, it is particularly preferable that Q in the above generalformula (II) is a group represented by the formula (III). And in theformula (III), it is preferred that R₈ and R₉ are independently ahydroxyalkyl group or an alkoxyalkyl group of 1-6 carbon atoms.

In the general formula (II), Q preferably forms a water-soluble groupand to give specific examples, a hydrogen atom, an alkyl group of 1-3carbon atoms (i.e., methyl, ethyl, propyl or isopropyl), a hydroxyalkylgroup of 1-3 carbon atoms and a hydroxyl group are particularlypreferred from the viewpoint of effective protection of inorganicmaterial layer, such as a polysilicon film, an amorphous silicon film,etc. against corrosion.

Specific examples of the benzotriazole-based compounds includebenzotriazole, 5,6-dimethylbenzotriazole, 1-hydroxybenzotriazole,1-methylbenzotriazole, 1-aminobenzotriazole, 1-phenylbenzotriazole,1-hydroxymethylbenzotriazole, 1-benzotriazole-methyl carboxylate,5-benzotriazole-carboxylic acid, 1-methoxybenzotriazole,1-(2,2-dihydroxyethyl)benzotriazole,1-(2,3-dihydroxypropyl)benzotriazole, and products of “IRGAMET” seriesmarketed from Ciba Speciality Chemicals such as2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol,2,2′-{[(5-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol,2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethane and2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bispropane. Amongthese compounds, it is particularly preferable to use1-(2,3-dihydroxypropyl)benzotriazole,2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol,2,2′-{[(5-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol, etc. Thebenzotriazole compounds may be used either individually or incombination.

The mercapto group containing compound is preferably of such a structurethat a hydroxyl group and/or a carboxyl group is present in eitherα-position or β-position on the carbon atom binding to the mercaptogroup. Specifically, preferred examples of such compound include1-thioglycerol, 3-(2-aminophenylthio)-2-hydroxypropylmercaptan,3-(2-hydroxyethylthio)-2-hydroxypropylmercaptan, 2-mercaptopropionicacid and 3-mercaptopropionic acid. Among these, 1-thioglycerol is usedwith particular preference. Mercapto group containing compounds may beused either singly or in admixture.

Component (d) is preferably chosen as appropriate for the fabricationprocess, more specifically, for the applicable device. The followingthree examples of the fabrication process may be mentioned:

(1) a photoresist pattern is formed on a substrate having an Al metallayer and after etching the substrate with said pattern being used as amask, ashing or other treatment is performed to strip away thephotoresist pattern, thereby forming Al metal wiring;

(2) in the dual damascene process, a multiple of Si-based interlevellayers such as low-dielectric films (e.g. SOG film) and insulation films(e.g. SiN layer and SiO₂ layer) are formed in superposition on a Culayer carrying substrate, and after etching the low-dielectric films andinsulation films with the photoresist pattern on the topmost layer beingused as a mask, the photoresist pattern is stripped away by ashing orother treatment to form via holes connecting to the Cu layer on thesubstrate;

(3) in the dual damascene process, after forming via holes by the methoddescribed in (2), a specified number of low-dielectric films, insulationfilms, etc. are etched with a new photoresist pattern on the topmost ofthe remaining superposed interlevel films being used as a mask, and thenashing or other treatment is performed to strip away the photoresistpattern while forming wiring grooves (trenches) that communicate withthe via holes.

Needless to say, these are not the sole examples of the fabricationprocess to which component (d) is applicable. Various approaches havebeen proposed for the dual damascene process and cases (2) and (3) arenot the sole examples that can be employed.

In case (1), the residues to be stripped away are mostly Al-based onesand the metal wiring to be protected against corrosion is made of an Al(inclusive of Al alloy) conductor. In a case like this, the aromatichydroxy compound is preferably used as component (d) particularly fromthe viewpoint of preventing the Al conductor from corrosion.

In case (2), the residues to be stripped are mostly Cu-based residuesthat form on the bottom of via holes and the wiring metals to beprotected against corroding are also mostly Cu-based ones. In a caselike this, the benzotriazole-based compound and the mercapto groupcontaining compound are preferably used.

In case (3), the residues are mostly Si-based ones and the wiring metalsto be protected against corroding are mostly Cu-based ones. In a caselike this, the benzotriazole-based compound and the mercapto groupcontaining compound are preferably used. From the viewpoint of efficientstripping of the Si-based residues, it is preferred to use thebenzotriazole-based compound in combination with the mercapto groupcontaining compound. Since the combination of the aromatic hydroxycompound, water and the amine is known to be capable of enhancedstripping of the Si-based residues, the aromatic hydroxy compound isalso used with preference in case (3).

If two or more of the three compounds mentioned above as component (d)are used in combination, they are each preferably compounded in anamount of about 0.5-10 mass percent, more preferably about 1-4 masspercent. If the amount of each compound is less than 0.5 mass percent,Al or Cu is prone to corrode. Even if the amount of each compoundexceeds 10 mass percent, there is no commensurate increase ineffectiveness. The upper limit for the total content of component (d) ispreferably no more than about 15 mass percent.

Water-soluble organic solvents as component (e) are not specificallyrestricted so long as it is miscible with water and other componentsemployed in the invention.

Examples of such water-soluble organic solvents include sulfoxides, suchas dimethyl sulfoxide; sulfones, such as dimethyl sulfone, diethylsulfone, bis(2-hydroxyethyl)sulfone and tetramethylene sulfone; amides,such as N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamide and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, propylene glycol monomethyl ether,propylene glycol monoethyl ether, propylene glycol monopropyl ether andpropylene glycol monobutyl ether. Among these examples, preferable onesare dimethyl sulfoxide, dimethylimidazolidinone, N-methyl-2-pyrrolidoneand diethylene glycol monobutyl ether. Component (e) may be used eitheralone or in combination with one another.

The amount of component (e) is balance of total amounts of othercomponents in the photoresist stripping solution of the invention.

The stripping solution of the invention may further contain, as anoptional component, an acetylene alcohol/alkylene oxide adduct preparedby adding an alkylene oxide to an acetylene alcohol.

As the acetylene alcohol as described above, use may be preferably madeof compounds represented by the following general formula (IV):

wherein R₁₀ is a hydrogen atom or a group represented by the followingformula (V):

and R₁₁, R₁₂, R₁₃ and R₁₄ are each independently a hydrogen atom or analkyl group having 1-6 carbon atoms.

These acetylene alcohols are commercially available under trade names of“Surfynol” and “Olfin” series (both are produced by Air Product andChemicals Inc.). Of these commercial products, “Surfynol 104”, “Surfynol82” or mixtures thereof are most preferred for the physical properties.Use can be also made of “Olfin B”, “Olfin P”, “Olfin Y” etc.

As the alkylene oxide to be added to the acetylene alcohol as describedabove, it is preferable to use ethylene oxide, propylene oxide or amixture thereof.

In the present invention, it is preferable to use, as the acetylenealcohol/alkylene oxide adduct, compounds represented by the followinggeneral formula (VI):

wherein R₁₅ is a hydrogen atom or a group represented by the followingformula (VII):

and R₁₆, R₁₇, R₁₈ and R₁₉ are each independently a hydrogen atom or analkyl group having 1-6 carbon atoms; (n+m) is an integer of 1 to 30,which is the number of ethylene oxide molecules added. This numbersubtly affects the properties of the compound such as water solubilityand surface tension.

The acetylene alcohol/alkylene oxide adducts per se are known assurfactants. These products are commercially available under the tradenames of “Surfynol” series (products of Air Product and Chemicals Inc.)and “Acetylenol” series (products of Kawaken Fine Chemicals Co., Ltd.)and have been appropriately utilized. Among these products, it ispreferred to use “Surfynol 440” (n+m=3.5), “Surfynol 465” (n+m=10),“Surfynol 485” (n+m=30), “Acetylenol EL” (n+m=4), “Acetylenol EH”(n+m=10) or mixtures thereof, in view of the changes in their physicalproperties such as water solubility and surface tension depending on thenumber of ethylene oxide molecules added. A mixture of “Acetylenol EL”with “Acetylenol EH” in a mass ratio of 2:8 to 4:6 is particularlydesirable.

Use of the acetylene alcohol/alkylene oxide adduct makes it possible toimprove the penetrating properties and wetting properties of thestripping solution.

When the stripping solution according to the invention contains theacetylene alcohol/alkylene oxide adduct, the amount thereof ispreferably 0.05-5 mass percent, more preferably 0.1-2 mass percent. Whenthe content exceeds the upper limit as defined above, it tends to causefoaming but the wetting properties cannot be improved any more. When thecontent is less than the lower limit as defined above, on the otherhand, the desired improvement in the wetting properties can be scarcelyestablished.

The photoresist stripping solution of the invention can advantageouslybe used with all photoresists, whether negative- or positive-working,that can be developed with aqueous alkaline solutions. Such photoresistsinclude, but are not limited to, (i) a positive-working photoresistcontaining a naphthoquinonediazide compound and a novolak resin, (ii) apositive-working photoresist containing a compound that generates anacid upon exposure, a compound that decomposes with an acid to have ahigher solubility in aqueous alkali solutions, and an alkali-solubleresin, (iii) a positive-working photoresist containing a compound thatgenerates an acid upon exposure and an alkali-soluble resin having agroup that decomposes with an acid to have a higher solubility inaqueous alkali solutions, and (iv) a negative-working photoresistcontaining a compound that generates an acid upon illumination withlight, a crosslinker and an alkali-soluble resin.

According to the invention, photoresists are stripped away by one of twomethods which have the following steps in common: forming a photoresistpattern by lithography on a substrate having conductive metallic layers,insulation layers and low-dielectric layers thereon, and selectivelyetching the layers with the photoresist pattern used as a mask to form afine-line circuit. After these steps, the photoresist pattern isimmediately stripped away (method I), or the etched photoresist patternis subjected to plasma ashing and thereby post-ashing residues, such asthe modified photoresist film (photoresist film residue) and metaldeposition, are stripped away (method II).

An example of method I in which the photoresist film is stripped awayimmediately after etching comprises:

(I) providing a photoresist layer on a substrate;

(II) selectively exposing said photoresist layer;

(III) developing the exposed photoresist layer to provide a photoresistpattern;

(IV) etching the substrate to form a pattern using said photoresistpattern as a mask; and

(V) stripping away the photoresist pattern from the etched substrateusing the photoresist stripping solution of the present invention.

An example of method II in which the modified photoresist film and metaldeposition resulting from plasma ashing are stripped away after etchingcomprises:

(I) providing a photoresist layer on a substrate;

(II) selectively exposing said photoresist layer;

(III) developing the exposed photoresist layer to provide a photoresistpattern;

(IV) etching the substrate to form a pattern using said photoresistpattern as a mask;

(V) plasma ashing the photoresist pattern;

(VI) stripping away the post-ashing residues from the substrate usingthe photoresist stripping solution of the present invention.

The metal wiring can typically be aluminum (Al) based wiring or copper(Cu) based wiring. The Cu wiring as used in the invention may be eitherCu alloy wiring that is mainly composed of Cu (in an amount of, say, atleast about 90 mass percent) and which contains Al and other metals, orpure Cu wiring.

In the second stripping method described above, residue adhere to thesubstrate surface after plasma ashing, such as photoresist residue(modified photoresist film) and metal deposition that formed duringetching of the metal film. These residues are contacted by the strippingsolution of the invention so that they are stripped away from thesubstrate surface. Plasma ashing is inherently a method for removing thephotoresist pattern but it often occurs that part of the photoresistpattern remains as a modified film; the present invention isparticularly effective for the purpose of completely stripping away suchmodified photoresist film.

In forming the photoresist layer, exposing, developing and etchingtreatments, any conventional means may be employed without particularlimitation.

After the development step (III) or the stripping step (V) or (VI),conventional rinsing may optionally be performed using pure water, loweralcohols, etc., followed by drying.

Depending on the type of photoresist used, post-exposure bake which isusually applied to the chemically amplified photoresist may beperformed. Post bake may also be performed after forming the photoresistpattern.

The photoresist is usually stripped by the dip, shower or paddle method.The stripping time is not limited to any duration as long as it issufficient to achieve removal of the photoresist.

If the metal wiring on the substrate is made of copper (Cu), the dualdamascene process may be mentioned as a preferred mode of using thephotoresist stripping solution of the invention. Specifically, themethod described above in the column “2. Description of the Related Art”may be mentioned as a preferred example of the dual damascene processbut needless to say, that is not the sole example of the dual damasceneprocess that can be adopted.

EXAMPLES

The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting. Unless otherwise noted, all compounding amounts are expressedby mass percent.

Examples 1-12 and Comparative Examples 1-14

A silicon wafer having an SiO₂ layer formed thereon was used as asubstrate (Si substrate). On this substrate, an Al—Si—Cu layer, a TiNfilm and a P-TEOS film (SiO₂ film deposited using tetraethylorthosilicate) were formed as the first, second and third layers,respectively. The topmost layer was spin-coated with a positive workingphotoresist (TDUR-P015 of Tokyo Ohka Kogyo Co., Ltd.), which wasprebaked at 90° C. for 90 seconds to form a photoresist layer 0.7 μmthick.

The photoresist layer was exposed through a mask pattern using FPA 3000EX3 (Canon Inc.), then subjected to post-exposure bake at 110° C. for 90seconds and developed with an aqueous solution of 2.38 mass percenttetraammonium hydroxide (TMAH) to form a pattern of holes 350 nm indiameter. Subsequently, post bake was performed at 110° C. for 90seconds, followed by dry etching and ashing.

The thus processed substrate was subjected to strip away post-ashingresidues with one of the photoresist stripping solutions (see Tables 1and 2) by either dipping (70° C.×30 min) or paddling (70° C.×2 min) (seeTable 3 for the specific treatment adopted) and subsequently rinsed withpure water. The strippability of the Si-based residue formed around theopening of each hole, the state of corrosion of the Al wiring at thebottom of each hole, and the state of corrosion of Si in the reversesurface of the Si substrate were evaluated by examination with an SEM(scanning electron microscope). The results are shown in Table 3.

The rating criteria for the respective evaluations were as follows.

[Strippability (of Si-Based Residue)]

A: No residue found (good strippability)

B: Some residue left (poor strippability)

[State of Corrosion (of the Reverse Surface of Si Substrate and AlWiring)]

a: No corrosion found

a′: Slight corrosion

b: Substantial corrosion TABLE 1 Photoresist stripping solution (masspercent) Component Component Component Component component Other (a) (b)(c) (d) (e) components Ex. 1 TBAH MEA (20) d1 + d2 NMP — (5) (20) (2 +3) (50) Ex. 2 TBAH MEA (20) d2 + d4 NMP — (2.5) (10) (5 + 2) (60.5) Ex.3 TPAH MEA (15) d1 + d3 + d4 DMF — (3) (15) (2 + 3 + 2) (60) Ex. 4 MTPAHMEA (20) d1 + d2 + d4 DMF — (5) (25) (2 + 3 + 2) (43) Ex. 5 MTBAH MMA(15) d4 + d5 DMI — (2.5) (22.5) (3 + 2) (55) Ex. 6 TPAH MMA (20) d2 + d4NMP — (5) (25) (3 + 2) (45) Ex. 7 TBAH MMA (20) d1 + d3 NMP — (8) (40)(2 + 3) (27) Ex. 8 TPAH MEA (40) d1 + d2 + d4 NMP — (5) (20) (2 + 3 + 2)(28) Ex. 9 TBAH MEA (40) d1 + d3 + d4 DMI — (5) (20) (2 + 3 + 2) (28)Ex. 10 TPAH DGA (38) d1 + d3 + d4 NMP — (5) (25) (2 + 3 + 2) (25) Ex. 11TPAH DGA (35) d1 + d4 NMP — (5) (30) (1 + 1) (28) Ex. 12 TPAH DGA (25)d1 + d2 + d4 NMP — (5) (40) (1 + 2 + 2) (25)

TABLE 2 Photoresist stripping solution (mass percent) ComponentComponent Component Component component Other (a) (b) (c) (d) (e)components Com. Ex. 1 TBAH MEA (20) d1 + d2 NMP —  (5) (60) (2 + 3) (10)Com. Ex. 2 TBAH MEA (20) d1 + d2 NMP — (10) (20) (2 + 3) (45) Com. Ex. 3— MEA (20) d1 + d2 DMSO TMAH (20) (2 + 3) (50) (5)   Com. Ex. 4 — MEA(20) d1 + d2 + d4 NMP TEAH (16) (2 + 3 + 2) (53) (4)   Com. Ex. 5 — MEA(20) d1 + d2 + d4 NMP CO (20) (2 + 3 + 2) (48) (5)   Com. Ex. 6 — DGA(15) d1 + d2 + d4 NMP MTEAH (25) (2 + 3 + 2) (48) (5)   Com. Ex. 7 — MEA(20) d1 + d2 DMI DMDEAH (10) (2 + 5) (60.5) (2.5) Com. Ex. 8 — MEA   (9.76) — DMI + DMSO TMAH  (9) (18 + 63)   (0.24) Com. Ex. 9 — MEA —d3 DMF — (10) (3) (87) Com. Ex. — MEA (32) — DEGE TMAH (3), 10 (35) (20)SRB (10) Com. Ex. — —   (8.0) — DEGE TMAH 11 (90) (2.0) Com. Ex. — MEA(28) — NMP TMAH 12 (40) (30) (2.0) Com. Ex. — MDA (69) — PG TMAH 13 (10)(10) (1.0) Com. Ex. — MEA (10) — NMP TMAH 14 (25) (57) (5)  

The symbols used in Tables 1 and 2 to indicate the respective componentshave the following definitions, which also apply to Table 4 set forthlater.

TBAH: tetrabutylammonium hydroxide

TPAH: tetrapropylammonium hydroxide

MTPAH: methyltripropylammonium hydroxide

MTBAH: methyltributylammonium hydroxide

TMAH: tetramethylammonium hydroxide

TEAH: tetraethylammonium hydroxide

CO: choline

MTEAH: methyltriethylammonium hydroxide

DMDEAH: dimethyldiethylammonium hydroxide

MEA: monoethanolamine

MMA: N-methylethanolamine

MDA: N-methyldiethanolamine

DGA: 2-(2-aminoethoxy)ethanol

d1: 2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol(IRGAMET 42)

d2: pyrogallol

d3: gallic acid

d4: 1-thioglycerol

d5: pyrocatechol

SRB: sorbitol

NMP: N-methyl-2-pyrrolidone

DMF: N,N-dimethylformamide

DMI: 1,3-dimethyl-2-imidazolidinone

DMSO: dimethyl sulfoxide

DEGE: diethylene glycol monoethyl ether

PG: propylene glycol TABLE 3 State of corrosion Strip- of the pabilityreverse State of of Si- surface of corrosion based Si of Al Condition ofresidue substrate wiring stripping step Ex. 1 A a a 70° C.-30 min(dipping) Ex. 2 A a a 70° C.-30 min (dipping) Ex. 3 A a a 70° C.-30 min(dipping) Ex. 4 A a a 70° C.-30 min (dipping) Ex. 5 A a a 70° C.-30 min(dipping) Ex. 6 A a a 70° C.-30 min (dipping) Ex. 7 A a a 70° C.-30 min(dipping) Ex. 8 A a a 70° C.-2 min (paddling) Ex. 9 A a a 70° C.-2 min(paddling) Ex. 10 A a a 70° C.-2 min (paddling) Ex. 11 A a a 70° C.-2min (paddling) Ex. 12 A a a 70° C.-30 min (dipping) Com. Ex. 1 A a  a′70° C.-30 min (dipping) Com. Ex. 2 A b a 70° C.-30 min (dipping) Com.Ex. 3 A b b 70° C.-30 min (dipping) Com. Ex. 4 A b b 70° C.-30 min(dipping) Com. Ex. 5 A b b 70° C.-30 min (dipping) Com. Ex. 6 A b b 70°C.-30 min (dipping) Com. Ex. 7 A b b 70° C.-30 min (dipping) Com. Ex. 8B a b 70° C.-30 min (dipping) Com. Ex. 9 B a a 70° C.-30 min (dipping)Com. Ex. 10 A b b 70° C.-30 min (dipping) Com. Ex. 11 B a b 70° C.-30min (dipping) Com. Ex. 12 A b b 70° C.-30 min (dipping) Com. Ex. 13 A bb 70° C.-30 min (dipping) Com. Ex. 14 B a b 70° C.-30 min (dipping)

The effect of using the aromatic hydroxy compound, benzotriazole-basedcompound and the mercapto group containing compound as component (e)either singly or in combination was checked in the following Examples.

Examples 13-19

[Substrate I]

Processed substrates were prepared by repeating the procedure employedin Examples 1-12.

The processed substrates were stripped away of the post-ashing residuesby dipping in photoresist stripping solutions (70° C.×30 min) consistingof 5 mass percent of tetrapropylammonium hydroxide (TPAH) as component(a), 20 mass percent of monoethanolamine (MEA) as component (b), 40 masspercent of component (c), and 30 mass percent of N-methyl-2-pyrrolidone(NMP) as component (e), plus 5 mass percent of component (d) (see Table4 for the specific compound used), followed by rinsing with pure water.The strippability of the Al-based residue formed on the sidewall of eachhole, the strippability of the Si-based residue formed around theopening of each hole, the state of corrosion of the Al wiring at thebottom of each hole, and the state of corrosion of Si in the reversesurface of the silicon wafer were evaluated by examination with an SEM(scanning electron microscope). The results are shown in Table 5.Symbols d1, d2 and d4 used in Table 4 have the same definitions as inTables 1 and 2.

[Substrate II]

A silicon wafer having a SiO₂ layer formed thereon was used as asubstrate (Si substrate). On this substrate, a Cu layer was formed in athickness of 0.5 μm. The thus processed substrate II was stripped awayof the post-ashing residues under the same conditions as for thesubstrate I and then rinsed with pure water. The state of corrosion ofthe Cu layer was evaluated by examination with an SEM (scanning electronmicroscope). The results are shown in Table 5.

The rating criteria for the evaluations summarized in Table 5 were asfollows:

[Strippability (of Al- and Si-Based Residues)]

⊚: Complete stripping

∘: Stripping was almost complete but there was a residue which would notinterfere with device operation; a long time was taken to remove itcompletely.

[State of Corrosion (of the Reverse Surface of Si Substrate, Al Wiringand Cu Layer)]

⊚: No corrosion found at all

∘: No corrosion was found that would interfere with device operation.

x: Very slight corrosion

These criteria correspond to subdivisions of rating A (forstrippability) and rating a (for the state of corrosion) that wereemployed in Examples 1-12. TABLE 4 Component (d) Mercapto groupBenzotriazole- Aromatic hydroxy containing based compound compoundcompound Ex. 13 d1 (2) d2 (3) - Ex. 14 d1 (2) - d4 (3) Ex. 15 - d2 (3)d4 (2) Ex. 16 d1 (2) d2 (1) d4 (2) Ex. 17 d1 (5) - - Ex. 18 - d2 (5) -Ex. 19 - - d4 (5)

TABLE 5 Substrate I State of State of corrosion cor- of the Substrate IIStrippability Strippability rosion reverse State of of Al- of Si- of Alsurface of corrosion of based based wiring Si Cu wiring residue residuelayer substrate layer Ex. 13 ⊚ ⊚ ⊚ ⊚ ⊚ Ex. 14 ⊚ ⊚ ⊚ ⊚ ⊚ Ex. 15 ⊚ ⊚ ⊚ ⊚ ⊚Ex. 16 ⊚ ⊚ ⊚ ⊚ ⊚ Ex. 17 ⊚ ◯ Δ ⊚ ⊚ Ex. 18 ⊚ ⊚ ⊚ ⊚ ◯ Ex. 19 ⊚ ◯ ◯ ⊚ ⊚

As described above in detail, according to the present invention, thereis provided a photoresist stripping solution that is suitable for use inthe photolithographic technology to form today's semiconductor andliquid-crystal display devices having an ever decreasing feature sizeand an increasing number of interlevel films superposed on the substrateand which can assure effective protection of Al, Cu and other wiringmetal conductors against corrosion as well as efficient stripping of thephotoresist film, post-ashing residues, and there is also provided aphotoresist stripping solution that is particularly suitable for use inthe formation of metal wiring on a substrate overlaid with Si-basedinterlevel films such as insulation films (e.g. SiO₂ film) andlow-dielectric films (e.g. SOG film) and by means of which efficientstripping of Si deposition originating from these Si-based interlevelfilms and effective protection of the substrate (particularly thereverse side of an Si substrate) from corrosion can be accomplished in abalanced way.

1. A photoresist stripping solution comprising (a) a quaternary ammoniumhydroxide of the following general formula (I):

where R₁, R₂, R₃ and R₄ are each independently an alkyl group or ahydroxyalkyl group, provided that at least one of R₁, R₂, R₃ and R₄ isan alkyl or hydroxyalkyl group having at least 3 carbon atoms, (b) awater-soluble amine, (c) water, (d) a corrosion inhibitor and (e) awater-soluble organic solvent, the compounding ratio of component (a) tocomponent (b) being in the range of from 1:3 to 1:10 by mass.
 2. Thephotoresist stripping solution according to claim 1, wherein component(a) is at least one compound selected from among tetrabutylammoniumhydroxide, tetrapropylammonium hydroxide, methyltributylammoniumhydroxide and methyltripropylammonium hydroxide.
 3. The photoresiststripping solution according to claim 1, wherein component (b) is atleast one compound selected from among monoethanolamine,2-(2-aminoethoxy)ethanol and N-methylethanolamine.
 4. The photoresiststripping solution according to claim 1, wherein component (d) is atleast one compound selected from among an aromatic hydroxy compound, abenzotriazole-based compound and a mercapto group containing compound.5. The photoresist stripping solution according to claim 4, wherein thearomatic hydroxy compound is at least one compound selected from amongpyrocatechol, pyrogallol and gallic acid.
 6. The photoresist strippingsolution according to claim 4, wherein the benzotriazole-based compoundis a compound represented by the following general formula (II):

where R₅ and R₆ are each independently a hydrogen atom, a substituted orunsubstituted C₁-C₁₀ hydrocarbon group, a carboxyl group, an aminogroup, a hydroxy group, a cyano group, a formyl group, a sulfonylalkylgroup or a sulfo group; Q is a hydrogen atom, a hydroxy group, asubstituted or unsubstituted C₁-C₁₀ hydrocarbon group, provided that itmay have an amido bond or an ester bond in the structure, an aryl groupor a group represented by the following formula (III)

where R₇ is a C₁-C₆ alkyl group; R₈ and R₉ are each independently ahydrogen atom, a hydroxy group or a C₁-C₆ hydroxyalkyl or alkoxyalkylgroup.
 7. The photoresist stripping solution according to claim 4,wherein the benzotriazole-based compound is at least one compoundselected from among 1-(2,3-dihydroxypropyl)-benzotriazole,2,2′-{[(4-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol and2,2′-{[(5-methyl-1H-benzotriazol-1-yl)methyl]imino}bisethanol.
 8. Thephotoresist stripping solution according to claim 4, wherein themercapto group containing compound is 1-thioglycerol.
 9. A method ofstripping photoresists comprising forming a photoresist pattern on asubstrate, etching the substrate using said photoresist pattern as amask, and thereafter stripping away the photoresist pattern from thesubstrate using the photoresist stripping solution according to claim 1.10. A method of stripping photoresists comprising forming a photoresistpattern on a substrate, etching the substrate using said photoresistpattern as a mask, then plasma ashing the photoresist pattern, andthereafter stripping away post-plasma ashing residues from the substrateusing the photoresist stripping solution according to claim
 1. 11. Themethod of stripping photoresists according to claim 9, wherein thesubstrate has either Al wiring or Cu wiring or both thereon.
 12. Themethod of stripping photoresists according to claim 9, wherein thesubstrate has an Si-based interlevel film thereon.
 13. The method ofstripping photoresists according to claim 9, wherein the substrate is anSi substrate.
 14. The method of stripping photoresists according toclaim 10, wherein the substrate has either Al wiring or Cu wiring orboth thereon.
 15. The method of stripping photoresists according toclaim 10, wherein the substrate has an Si-based interlevel film thereon.16. The method of stripping photoresists according to claim 10, whereinthe substrate is an Si substrate.